The multi-hop wireless network communication technology is a technology by which a wireless station exchanges data with the desired wireless station via multiple wireless stations installed as relay stations between the wireless stations by multi-hop communication.
In multi-hop communication, a wireless station does not directly wirelessly communicate with the desired window station but wirelessly communicates therewith via relay stations. Accordingly, multi-hop communication is a communication technology that is effective, for example, when an obstacle to radio waves is present.
Particularly in recent years, the cost of wireless communication devices for wireless LAN (local area network) or the like has been reduced, and sensor network technologies such as Bluetooth®, which is a short-range wireless communication standard mainly for digital devices, and ZigBee, which is a short-range wireless communication standard mainly for household electrical appliances, have been standardized. Accordingly, expectation for application of wireless technologies to the industry field has been increased, increasing application cases.
The multi-hop wireless network technology is expected to contribute to reductions in the number of monitoring/control cables by applying it to the industry field, for example, social infrastructure business, such as electric power or transportation, and monitoring/control networks for the manufacturing industry, such as factory automation (FA) systems and process automation (PA) systems.
Further, making wired cables wireless can result in reductions in the cost of cable installation or maintenance cost for a routine check.
Furthermore, use of wireless technologies allows business entities to more flexibly deal with changes in operation, such as addition of equipment or a change in the configuration of equipment.
As seen, wireless network systems have many advantages. On the other hand, application of wireless real-time communication to the industry field requires high reliability, and a failure that occurs in a wireless network must be dealt with rapidly.
For example, assume that a wireless network that meets a requirement by obtaining multiple channels, for example, two communication paths by multi-hop communication is constructed. In this case, at the point in time when one communication path fails, the reliability of the other communication path will decrease. For this reason, in the construction of a communication path, it is necessary to design favorable communication paths that are insusceptible to a failure to the extent possible.
In the field of industry, it is particularly important to construct or design communication paths of a wireless network in a building.
A wireless environment in a building is significantly susceptible to the floor plan of the building, the height of the ceiling, material characteristics of the wall, ceiling, and floor, the size of an opening such as the door or window, furniture or equipment inside the building, and the like. The wireless environment also shows characteristics that are different among sites over which a wireless network is to be constructed. Accordingly, a wireless network must be constructed or designed considering these factors.
For this reason, it is desired to actually measure the propagation state of a radio wave at locations where a wireless base station can be installed, of the sites over which a wireless network is to be constructed and to design the layout of wireless base stations on the basis of the measurement results.
However, it is difficult to actually measure the propagation state of a radio wave in all parts of space in the building in terms of cost and time. For this reason, it is practical and effective to design the layout of wireless base stations in a building into which wireless base stations are to be introduced newly, on the basis of the layout design of wireless base stations in a building in which a wireless network is already constructed, instead of measuring the propagation state of a radio wave thoroughly as described above.
The present invention relates to a technology of constructing a wireless network in a new building using an already constructed wireless network as described above.
Methods for estimating the propagation of a radio wave include a method of using a statistical model based on values which are actually measured at various locations. In addition, Japanese Unexamined Patent Application Publication No. 2009-296572 (Patent Literature 1) and the like have proposed methods for estimating radio wave propagation characteristics. These technologies are configured to, in the installation of wireless base stations into a wide area, estimate the installment locations of wireless base stations using existing radio wave propagation characteristics.
In a building, however, there are large differences in structure among sites. Accordingly, to construct a wireless network system which is required to have high reliability, it is important to design a wireless network considering a propagation environment specific to each site.